Ascertainment of the level of the slag layer on a metallurgical melt is vital for many purposes, especially in the refining of steel where the slag overlies a bath of molten steel or iron in a converter or like vessel. This knowledge is essential for monitoring the progress of the refining operation and from a safety viewpoint to prevent overflow of the slag from the converter.
Various systems have been provided heretofore for measuring slag levels or the like, including the systems described in my U.S. Pat. Nos. 4,098,128 and 4,175,612. In addition, the assignee of the instant application has also developed a system for measuring the level of slag which permits a concurrent determination of the consistency thereof, thereby providing significant information, e.g. for the refining of phosphorus melts and where frothy slags are deemed to be desirable.
This system, described in Luxembourg Pat. No. 71,261, comprises a thermostatically temperature-controlled acoustic conduit which is disposed above the converter and which captures the noise emitted or generated by the lance which blows the melt with oxygen.
After filtering foreign frequencies from the electrical signals resulting from the noise detection, one can obtain a signal which, with appropriate interpretation, can represent the noise absorbed by the slag and hence the degree of the frothy character thereof as well as the position of the slag layer in the converter.
However, this system cannot be used with more elaborate refining processes as are described in an application for patent in Luxembourg No. 81,207 filed Apr. 30, 1979. As pointed out in this document, in addition to blowing of oxygen onto the surface of the melt, splashing is generated by the introduction of a mixing gas at the bottom of the vessel or crucible. This results in a slag of a nonfrothy consistency which is highly advantageous with respect to the post combustion of carbon monoxide above the bath. The disappearance of a frothy slag, however, eliminates the possibility of obtaining effective level and consistency measurements using the previously mentioned techniques.
The more dense slag resulting from bottom blowing of the melt with inert gas and the bubbling or splashing of and through the melt, requires another approach than noise absorption or like acoustic techniques for ascertaining the physical parameter or level of the melt.